This invention is generally related to a personal communications device having global positioning system receiver provisions which are clocked via a clock signal derived from a clock source shared with CDMA based radio. More particularly, the invention provides for a fractional N-synthesizer for providing a feedback signal for controlling an oscillator signal output frequency.
Personal communications devices incorporating global positioning (GPS) capabilities are becoming popular. In these devices, the circuitry and components necessary to provide the global positioning capabilities must share the same enclosure and circuit board real estate as the circuitry and components dedicated to providing, for example, mobile (cellular) telephone capabilities. Further, circuitry and components for both, GPS capabilities as well as mobile telephone capabilities are powered by the same power source, typically, via an on-board battery. While battery technology is improving, it is typical that the more power consumed by a device the larger the physical size of the battery necessary to provide a given operating time.
The demand for smaller, more compact personal communication devices is increasing. Concurrent with this increasing demand for compactness is the demand for devices that provide for increased functionality and capabilities. As functionality and capabilities increase, typically, so does the need for power and printed circuit real estate within the personal communications device.
In personal communications devices such as that shown in the block diagram of FIG. 1, wherein there is provided a personal communications device that incorporates a global positioning systems (GPS) receiver 100 and a code division multiple access (CDMA) based telecommunications device 200, it is common for separate clock sources (oscillators) to be associated with the GPS receiver 100 and the CDMA device 200. More particularly, GPS receiver 100 includes an associated oscillator 101 while CDMA device 200 includes an associated oscillator 201. Each oscillator, 101 and 201 provides a clock signal to the respective circuitry to which it is associated.
FIG. 2 shows a GPS receiver 100, which includes an oscillator 101. Oscillator 101 provides a signal of a particular frequency to phase comparator 146. Phase comparator 146 also receives input from frequency divider 136 and outputs a signal to loop filter 145. Loop filter 145 provides a signal to voltage controlled oscillator (VCO) 115 which generates an output signal whose frequency is contingent upon the signal input from loop filter 145. The signal from VCO 115 is provided to mixer 110 where it is combined with a radio frequency (RE) signal from low noise amplifier (LNA) 105 to produce a first intermediate frequency (EF) signal S1. The first IF signal S1 is provided to variable amplifier 112 and then on to mixer 120 and mixer 121. In mixer 120, the signal S1 is combined with a signal S2 from frequency divider 130 to produce an in-phase second IF frequency output signal S3. In mixer 121, the signal S1 is combined with a signal S4 from frequency divider 130 to produce a quadrature phase second IF frequency output signal S5. Signal S3 is provided to comparator and A to D processor 125 to produce a digitized signal 1 for output to GPS baseband section 150. Signal S5 is provided to comparator and A to D processor 126 to produce a digitized signal Q for output to GPS baseband section 150. Frequency divider 130 also provides its output signal S4 to frequency divider 135 and frequency divider 136. The output from VCO 115 is also provided to the frequency divider 130. Frequency divider 130 outputs a signal S4 that is mixed by mixer 121 with a signal S1 to produce a signal S5.
As two separate oscillators are provided within the same personal communications device 10, printed circuit board and/or integrated circuit real estate is devoted to accommodating each oscillator. Another disadvantage is that power consumption of the two oscillators is greater than for one oscillator. Thus it is desirable to have a personal communications device that overcomes the stated disadvantages.
This invention is directed to a personal telecommunications device having both global positioning systems (GPS) and telecommunications provisions that share a common clock source. GPS provisions include a feedback loop for controlling an oscillator generating a GPS system signal based upon the common clock signal. The feedback loop includes a frequency synthesizer for generating a feedback control signal, a phase comparator for generating a control signal in accordance with the feedback signal and the common clock signal, and a loop filter for processing and outputting the control signal to the oscillator to control the frequency of GPS system signals.
The invention provides a system for providing a clock signal to a global positioning system (GPS) receiver based upon a common clock source. In the architecture, the system may be implemented with a personal communications system that includes a telecommunications unit, a global positioning systems (GPS) receiver, and a common clock source for providing a clock signal to the global positioning receiver and the telecommunications unit. The GPS receiver includes a frequency synthesizer for providing a feedback signal for controlling an oscillator to provide a GPS system clock signal.
The invention can also be viewed as providing a method for a system clock signal to a GPS receiver. In this regard, the method can be broadly summarized by the following steps: receiving a clock signal from a clock source; generating a control voltage for controlling the frequency of an oscillator signal generated by an oscillator based upon a feedback signal from a frequency synthesizer; and generating a system clock signal of a particular frequency in response to the control voltage.